Localization you run yourself.

Why Rosetta

The math

Lingo.dev's published plans next to Rosetta. With Rosetta you still pay for tokens, but directly to your model provider, with no cap and no markup.

Lingo.dev figures are from lingo.dev/pricing as of September 2026. Enterprise pricing is custom.

Get started

Requires Node 20+. Works with any JSON/JSONC locale files (next-intl, i18next, vue-i18n, …). Prefer to hand it off? Your AI agent can do all of this.

1. Install

   Add Rosetta as a dev dependency. The package is rosetta-i18n, and it installs arosetta command.

   Copy install command

   npm install -D rosetta-i18n@next

2. Create the config

   init finds your source files (messages/en.json,locales/en/*.json, pages.en.json, …), infers target locales from the files next to them, and writes .rosetta/config.json. Coming from Lingo.dev? Use--from-lingo.

   Copy init command

   npx rosetta init
   # or: npx rosetta init --pattern messages/en.json --target es,fr,de
   # or: npx rosetta init --from-lingo

3. Tune the engine

   Pick a model and give it your brand voice and never-translate terms. Add lockedKeysfor anything that must stay identical (URLs, prices), and a context per file.

   .rosetta/config.json

   {
     "sourceLocale": "en",
     "targetLocales": ["es", "fr", "de", "ja", "pt-BR", "zh-CN"],
     "files": [
       { "pattern": "messages/en.json", "context": "Acme web app UI" }
     ],
     "engine": {
       "model": "anthropic/claude-sonnet-4.5",
       "brandVoice": { "*": "Friendly, plain, and direct." },
       "glossary": { "*": { "Acme": "Acme" } }
     }
   }

4. Add your model key

   Rosetta has no key of its own. Use your OpenRouter key, or point engine.baseURL at any OpenAI-compatible endpoint and set engine.apiKeyEnv to its variable.

   export OPENROUTER_API_KEY=sk-or-...

5. Preview, then push

   status shows what would happen, with no key and no cost. The first pushadopts your existing translations for free and translates only what's missing, changed, or broken.

   Copy commands

   npx rosetta status   # es  3 to translate · 412 to adopt
   npx rosetta push     # writes locale files + .rosetta/lock.json

6. Commit, then keep it in sync

   Commit .rosetta/ with your locale files. From then on it'sedit English → push → commit, run yourself, by an agent, or by the GitHub Action.

   .github/workflows/i18n.yml

   # .github/workflows/i18n.yml
   on:
     pull_request:
     push: { branches: [main] }
   jobs:
     i18n:
       runs-on: ubuntu-latest
       steps:
         - uses: actions/checkout@v4
         - uses: ian/rosetta@v1.0.0-beta.1
           with:
             # PRs: check (no key needed). main: translate + open a PR.
             mode: ${{ github.event_name == 'pull_request'
               && 'check' || 'pull-request' }}
           env:
             OPENROUTER_API_KEY: ${{ secrets.OPENROUTER_API_KEY }}

Or let your AI agent set it up

This prompt has your agent find your locale files and current setup, configure Rosetta, adopt your existing translations, report any that are broken today, wire up CI, and open one PR. It checks with you before anything expensive.

Set up Rosetta (npm: rosetta-i18n) for translations in this repo. Follow https://raw.githubusercontent.com/ian/rosetta/main/skills/rosetta/SKILL.md step by step: discover our locale files and current translation setup and report back, configure .rosetta/config.json, adopt our existing translations with `rosetta status` + `rosetta push` (list any translations it flags as broken), add tests and CI, remove the old translation tooling, document the workflow in AGENTS.md, and open one PR. Ask me before running `push --force`, before any large translation run, and before choosing how translations land if it's unclear.

For everyday requests ("add a German string", "why is the i18n job red?"), install the Rosetta skill. For agents that can't fetch URLs, use the self-contained prompt.

How it works

Rosetta keeps a lockfile, .rosetta/lock.json, that records a fingerprint of the source string behind every translation. On each push, every key is translated, retranslated, kept, adopted, copied, or removed, and nothing else is touched.

Questions